Security and/or valuable documents, such as identity cards, passports, access allowance cards, visas, tickets, driver licenses, vehicle documents, personalized valuables, credit cards, or personalized chip cards increasingly comprise electronic circuits and other active and passive electronic components, such as integrated semiconductors (ICs), but also chip modules, displays, batteries, coils, capacitors, contact spots etc.
When integrating such components in a card composite, for instance for thin semiconductor structures, the problem of the premature destruction or reduction of life of the component during the lamination by thermal and mechanical overload or load is encountered. With known methods, for instance for manufacturing polycarbonate (PC) Smart Cards during the lamination of individual film layers, a PC film is directly positioned over the chip. In the industrially established procedure, the prepared card structures are compressed, with simultaneous exposure to temperature and pressure, so to form a “quasi-monolithic” block. Since PC due to its specific heat transfer coefficient and its relatively high glass temperature Tg does not immediately flow sufficiently well, there is directly at the chip an increased mechanical pressure, which in most cases will lead to the mechanical destruction of the chip.
For avoiding this problem, it is known in the art to apply on the electronic components self-adhesive or elastic protective layers, in most cases thermoelastic and/or thermoplastic protective layers, for instance thermoplastic polyurethane (TPU), whereby the PC films with interposed components, such as chips, can be joined without a high risk of destruction for the component so to form a card. Normally, these adhesive layers are however a point of weakness of the card structure. Through the edge of the card, water vapor and air can more easily diffuse in and thus lead to a later delamination. Other environmental effects, too, in particular high temperatures, but also fast temperature changes may lead to that the card is split and therefore cannot be used anymore.
Moreover, self-adhesive films having a thickness <50 μm are difficult to handle or not at all on an industrial scale and are inflexible, if e.g. cavities are to be filled up. Similar considerations apply for components with diffractive structures, e.g. volume holograms. If the hologram is directly laminated with other PC films so to form a card, this occurs in certain cases under losses being quantifiable visually and by machine of the display quality of the hologram, in particular of the colors and of the 3-dimensional appearance. Most volume holograms based on photopolymer namely have a softening point or a glass temperature Tg of clearly below 150° C. If during the lamination the PC films being still hard at the beginning are pressed onto the soft photopolymer of the hologram, the Bragg planes are shifted, and certain elements appear shifted in wavelength. For instance, green picture elements become yellow picture elements, etc. Especially for volume holograms, further, the 3-dimensional impression is distinctly reduced, and the holograms appear rather flat and 2-dimensional and washed out. These effects, too, are based on the problem that the “hard” PC either comes on brittle faces and causes mechanical stress, or deforms softer objects, for instance of a photopolymer, whereby these components are impaired in their operation.
However, the base polymers used for the protective layers have different structures from the polycarbonate preferred for the other polymer layers, so that a substance-to-substance connection is sometimes not achieved during the lamination. There is, therefore, here too the risk of delamination. Consequently, there is an increased risk of counterfeit and/or manipulation, since the inlay can possibly be removed in a non-destructive manner and can be incorporated in a different layer composite, a counterfeit. Furthermore, data that the inlay carries or comprises can be manipulated.
From other technological sectors, latent-reactive adhesives are known in the art, and as an example only reference is made to the document EP 0 922 720 A1.